1. Field of the Invention
The present invention relates to a servo motor starting control method, and more particularly to a starting control method for detecting a starting angle position of a rotor of a servo motor by using an incremental encoder instead of a Hall device.
2. Related Art
With the rapid progress of technologies, the controlling function of a servo motor plays a quite important role in both conventional industry and high-tech industry. In contrast, as the chip manufacturing technologies have been improved, it is an inevitable trend to develop towards the directions of multi-function, high performance, and low cost in the field of controlling the servo motor. Currently, the development direction of the servo motor driver mainly lies in improving the performance of the driver and reducing the cost. The consideration of the cost and the demand for reducing the cost are correspondingly increased while improving the performance and enhancing the functions. In the servo driver, the demand for the position of the servo motor is quite important, and if an angle position of the servo motor fails to be obtained, the servo motor cannot be controlled highly efficiently.
Currently, the starting angle position of the servo motor is mostly obtained by using an incremental encoder installed with a Hall sensor. A typical servo motor driving circuit may be obtained with reference to FIG. 1, and FIG. 1 is a schematic view of a servo motor driving circuit in the prior art. When a motor 100 is initially rotated, a Hall sensor in an encoder 110 detects the motor 100, outputs phase change signals (U, V, and W), and then outputs rotor rotation signals (A, B, and Z), so as to feed back a rotation control associated message required by a servo driver 120. The phase change signals (U, V, and W) output by the encoder 110 are received and processed by a signal processing circuit 121, and then provided to a control unit 130 for estimating a position of the motor. The control unit 130 stores a firmware program. In the program, firstly, an initial position of the motor is estimated according to the phase change signals (U, V, and W) (Step 131); next, a current is adjusted according to a command (Step 132), and the adjusted current is output to a current control circuit 122 to control the rotation of the motor; and then, it is detected whether the phase change signals (U, V, and W) are changed or not (Step 133). Specifically, if the phase change signals (U, V, and W) are changed, the position of the motor is corrected according to the phase change signals (U, V, and W) (Step 134), and if the phase change signals (U, V, and W) are not changed, the position of the motor is corrected according to the rotor rotation signals (A, B, and Z) (Step 135).
The above-mentioned example is a typical technique for estimating the position by using the encoder installed with the Hall device, such that the incremental encoder in the common servo motor driver is configured with a circuit interface for the Hall device, and a control board is also configured with a chip for processing signals of the Hall device. Therefore, in consideration of reducing the cost, if the Hall device can be omitted, an area of the circuit board is reduced, and a cost of a connector on the circuit interface for the Hall device, a cost of the chip for processing the signals, and a cost of signal transmission lines are all reduced. However, if the Hall device is not used, an initial angle of the rotor cannot be obtained. Thus, if a method for obtaining a starting angle is provided, the above costs can be saved, and a stability of the driver can be improved. The more the elements on the circuit board are, the lower the stability of the driver will be. Once a problem occurs to the driver, the debugging procedure is rather complicated, and the maintenance cost is increased accordingly. If the chip and interface associated with the Hall device are not used, not only the stability is improved, but also the maintenance cost is lowered. Therefore, if a method capable of detecting the starting angle position of the servo motor is provided, and in the method, the motor is not required to rotate or is only required to slightly rotate during the detection, great economic benefits will be brought to the driver manufacturers. Moreover, as for the sensing motor driver manufacturers, the existing encoder interface can be used, and as long as a start detecting procedure is added in terms of software, the controlling function of the servo motor can be realized without affecting the reliability of the driver.
In addition, in the prior art, the starting position of the motor is estimated by using the UVW signals of the Hall device in the encoder, which is restricted by the amount of Hall devices, and it can only obtain that the most possible angle region of the motor is one of the six regions, so that the accuracy cannot be improved along with the practical demands, the element cost of the encoder is increased due to the Hall device, and the assembling cost of the encoder is increased as well.